Recently, interests in energy storage technology have been gradually increased. As the use of batteries is enlarged to applications for the storage of energy for portable telephones, camcorders, notebook computers, personal computers and electric vehicles, efforts on the research and development of batteries are increasingly embodied. In this view, the field of electrochemical devices receives the greatest attention, and among them, interests in the development of chargeable/dischargeable secondary batteries are focused. More recently, in the development of such batteries, active studies have been conducted to design a novel electrode and battery, which provide an improved capacity density and specific energy.
Among secondary batteries which are now in use, lithium secondary batteries developed in the early 1990s are in the spotlight due to the advantages of higher drive voltages and far greater energy densities than those of conventional batteries, such as Ni-MH, Ni—Cd and sulfuric acid-lead batteries. To obtain such a high drive voltage, it is necessary to provide an electrolyte composition that is stable in a charge/discharge voltage ranging from 0 to 4.2V.
A lithium secondary battery includes a cathode, an anode and an electrolyte. Upon the first charge cycle, lithium ions are deintercalated from a cathode active material. Then, the lithium ions are intercalated into an anode active material such as carbon particles, and are deintercalated from the anode active material upon discharge. In this manner, lithium ions transfer energy while they reciprocate between the cathode and the anode, thereby allowing the battery to be charged/discharged. Such lithium batteries show a problem in that they causes degradation in the battery quality during repeated charge/discharge cycles. The aforementioned problem becomes more serious as the battery has a higher capacity density. Moreover, although there may be a difference depending on the kind of the electrolyte used in a battery, in most cases, the electrolyte may decompose on the surface of the cathode and/or the anode, resulting in degradation in the quality and safety of the battery.
To solve the above problems, there has been a continuous need for a method of improving the cycle life characteristics of a battery by using an additive for non-aqueous electrolytes.
Japanese Patent Publication No. 2000-331709 disclose the use of a lactide as an additive for electrolytes in a method of increasing the charge/discharge efficiency of a lithium secondary battery and improving the cycle life characteristics of a lithium secondary battery. In this patent, it is thought that the lactide is effective for inhibiting the decomposition of an electrolyte in an anode formed of graphite.
Additionally, Japanese Laid-Open Patent No. 1995-192761 discloses the use of a lactide as an additive for electrolytes in a method of inhibiting the self-discharge of a lithium secondary battery and improving the high-temperature storage characteristics and cycle life characteristics of a lithium secondary battery. In this case, it is thought that the lactide inhibits the production of HF in an electrolyte by removing moisture.